Friction stir welding apparatus and associated thermal management systems and methods

ABSTRACT

The present invention provides a friction stir welding apparatus and associated thermal management systems and methods for joining one or more similar or dissimilar materials forming a workpiece along a joint to be welded. The friction stir welding apparatus includes a pin tool apparatus selectively disposed adjacent to and in direct contact with a first surface of the workpiece along the joint to be welded and a heating member disposed adjacent to a second surface of the workpiece along the joint to be welded, the heating member operable for controllably heating at least a portion of the workpiece adjacent to the joint to be welded. The friction stir welding apparatus also includes an annular spindle having an interior portion and an axis, the interior portion of the annular spindle at least partially defining one or more cooling channels, the one or more cooling channels operable for containing a cooling fluid. The friction stir welding apparatus further includes a shoulder disposed adjacent to the annular spindle and substantially aligned with the axis of the annular spindle and a pin tool disposed adjacent to the shoulder and substantially aligned with the axis of the annular spindle. The cooling fluid is operable for cooling at least one of the shoulder and the pin tool.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

The U.S. Government may have certain rights in the present inventionpursuant to U.S. Air Force Contract No. F33615-99-2-5215.

FIELD OF THE INVENTION

The present invention relates generally to a friction stir weldingapparatus. More specifically, the present invention relates to afriction stir welding apparatus and associated thermal managementsystems and methods.

BACKGROUND OF THE INVENTION

Friction stir welding is a solid-state joining technique that is wellknown to those of ordinary skill in the art. Typically, friction stirwelding is used to join difficult-to-weld metals, metal alloys (such asaluminum alloys, titanium alloys, nickel alloys, and the like), andother materials. For example, certain aluminum alloys are sensitive in aplasticized heat-affected zone, where the base metal reachestemperatures between solidus and liquidus during welding. In thisheat-affected zone, partial melting at grain boundaries forms a networkcontaining brittle compounds. As a result, weld ductility issubstantially reduced. Likewise, other conventional joining techniquesmay create geometric distortions near a weld joint due to hightemperature gradients induced in a workpiece during welding. Thesegeometric distortions may cause warping and other dimensional defects inthe workpiece, as well as residual stresses that may cause prematurefailure by cracking in the heat-affected zone or weld joint, lamellartearing, or by stress-corrosion cracking in some metals and metalalloys.

Friction stir welding techniques overcome many of the problemsassociated with other conventional joining techniques. In friction stirwelding, a rotating, cylindrical, non-consumable pin tool is plungedinto a rigidly clamped workpiece and traversed along the joint to bewelded. The pin tool is specially designed to provide a combination offrictional heat and thermo-mechanical working to accomplish the weld. Asthe pin tool is traversed along the joint to be welded, the plasticizedmetal, metal alloy, or other material is transferred from the leadingedge of the pin tool to the trailing edge of the pin tool, forming astrong solid-state weld joint in the wake of the pin tool. During thefriction stir welding of hard metals, metal alloys, and other materials,relatively high temperatures are generated in the pin tool, as well asthe tool holder. These relatively high temperatures in the pin tool, incombination with relatively low temperatures in the workpiece, mayresult in a weld joint of poor quality and mechanical integrity, proneto defects and workpiece distortions. For example, solid-state welds,including inertia welds, translational friction welds, and the like,associated with titanium alloys, such as Ti 17 and the like, aretypically characterized by poor fracture toughness and impact strength.This is due, in part, to the relatively high cooling rate of such weldsusing conventional joining techniques, including conventional frictionstir welding techniques.

Thus, what is needed are thermal management systems and methods thatallow a workpiece to be controllably heated during friction stirwelding, such that the temperatures in the workpiece more closely matchthe temperatures in the pin tool. In this manner, the cooling rate of aweld joint may be controlled. This would result in a weld joint ofenhanced quality and mechanical integrity, free from defects andworkpiece distortions and demonstrating improved fracture toughness,impact strength, and fatigue properties. This would also allow forenhanced pin tool temperature control in the event that a consumable pintool is used and minimize problems associated with pin tool debrisentrapment. Finally, pin tool wear would be reduced and pin tool lifeincreased.

BRIEF SUMMARY OF THE INVENTION

In various embodiments, the present invention provides thermalmanagement systems and methods that allow a workpiece to be controllablyheated during friction stir welding, such that the temperatures in theworkpiece more closely match the temperatures in the pin tool. In thismanner, the cooling rate of a weld joint may be controlled. This resultsin a weld joint of enhanced quality and mechanical integrity, free fromdefects and workpiece distortions and demonstrating improved fracturetoughness, impact strength, and fatigue properties. This also allows forenhanced pin tool temperature control in the event that a consumable pintool is used and minimizes problems associated with pin tool debrisentrapment. Finally, pin tool wear is reduced and pin tool lifeincreased.

In one embodiment of the present invention, a friction stir weldingapparatus operable for joining one or more similar or dissimilarmaterials forming a workpiece along a joint to be welded includes a pintool apparatus selectively disposed adjacent to and in direct contactwith a first surface of the workpiece along the joint to be welded and aheating member disposed adjacent to a second surface of the workpiecealong the joint to be welded, the heating member operable forcontrollably heating at least a portion of the workpiece adjacent to thejoint to be welded.

In another embodiment of the present invention, a thermal managementsystem for use with a friction stir welding apparatus operable forjoining one or more similar or dissimilar materials forming a workpiecealong a joint to be welded includes a heating member disposed adjacentto a surface of the workpiece along the joint to be welded, the heatingmember operable for controllably heating at least a portion of theworkpiece adjacent to the joint to be welded.

In a further embodiment of the present invention, a friction stirwelding method for joining one or more similar or dissimilar materialsforming a workpiece along a joint to be welded includes selectivelydisposing a pin tool apparatus adjacent to and in direct contact with afirst surface of the workpiece along the joint to be welded, disposing aheating member adjacent to a second surface of the workpiece along thejoint to be welded, and controllably heating at least a portion of theworkpiece adjacent to the joint to be welded using the heating member.

In a still further embodiment of the present invention, a thermalmanagement method for use with a friction stir welding method forjoining one or more similar or dissimilar materials forming a workpiecealong a joint to be welded includes disposing a heating member adjacentto a surface of the workpiece along the joint to be welded andcontrollably heating at least a portion of the workpiece adjacent to thejoint to be welded using the heating member.

In a still further embodiment of the present invention, a friction stirwelding apparatus operable for joining one or more similar or dissimilarmaterials forming a workpiece along a joint to be welded includes anannular spindle having an interior portion and an axis, the interiorportion of the annular spindle at least partially defining one or morecooling channels, the one or more cooling channels operable forcontaining a cooling fluid. The friction stir welding apparatus alsoincludes a shoulder disposed adjacent to the annular spindle andsubstantially aligned with the axis of the annular spindle and a pintool disposed adjacent to the shoulder and substantially aligned withthe axis of the annular spindle. The cooling fluid is operable forcooling at least one of the shoulder and the pin tool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional end view of one embodiment of the thermalmanagement system for friction stir welding of the present invention,illustrating the use of a ceramic strip heater disposed adjacent to ajoint to be welded and inert gas shielding;

FIG. 2 is a sectional end view of another embodiment of the thermalmanagement system for friction stir welding of the present invention,illustrating the use of a ceramic strip heater disposed adjacent to ajoint to be welded and powder shielding;

FIG. 3 is a sectional end view of a further embodiment of the thermalmanagement system for friction stir welding of the present invention,illustrating the use of a plurality of ceramic strip heaters and a hardmetal backing strip disposed adjacent to a joint to be welded and eitherinert gas or powder shielding; and

FIG. 4 is a sectional end view of a still further embodiment of thethermal management system for friction stir welding of the presentinvention, illustrating the use of a hard metal backing strip that isresistance heated disposed adjacent to a joint to be welded and eitherinert gas or powder shielding.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, in one embodiment of the present invention, afriction stir welding apparatus 10 includes a conventional or novel pintool apparatus 12 and a thermal management system 14. Optionally,elements of the thermal management system 14 are incorporated into thepin tool apparatus 12. The pin tool apparatus 12 includes a rotating pintool 16 that is selectively plunged into a rigidly clamped workpiece 18consisting of two similar or dissimilar materials 20,22 disposedadjacent to one another and forming a joint 24 to be welded. Thematerials 20,22 include, for example, one or more metals, metal alloys(such as aluminum alloys, titanium alloys, nickel alloys, or the like),or other materials. In a typical application, the workpiece 18 has athickness of between about 0.04 inches and about 1.5 inches, and thejoint 24 to be welded has a length of between about 1 inch and about 300inches or longer. Other thicknesses and lengths may, however, be used.For example, the joint 24 to be welded may have an infinite length, havea complex path and/or curvature, be circumferential in nature, etc.Preferably, the pin tool 16 has a substantially cylindrical or conicalshape and, optionally, includes a plurality of threads, truncations,and/or a radius tip. Conventional pin tools 16 are non-consumable,although a consumable pin tool 16 may be used. The pin tool 16 may bemade of a material that is similar to or dissimilar from thosecomprising the workpiece 18, such as a refractory metal alloy (amolybdenum alloy, a tungsten alloy, etc.) or the like. For afull-penetration weld, the diameter and length of the pin tool 16 areabout equal to the thickness of the workpiece 18, before being partiallyor wholly incorporated into the weld in the case of a consumable pintool 16. For a partial-penetration weld, the diameter and length of thepin tool 16 are smaller than the thickness of the workpiece 18, beforebeing partially or wholly incorporated into the weld in the case of aconsumable pin tool 16. Typically, the pin tool 16 is rotated at a speedof between about 100 rpm and about 1,500 rpm during friction stirwelding, depending upon the materials 20,22 to be welded, via a drivemechanism (not shown). It should be noted that the rotational speed ofthe pin tool 16 is also dependent upon the thickness of the workpiece 18to be friction stir welded, with thinner sections requiring higherrotational speeds and thicker sections requiring lower rotationalspeeds.

The pin tool 16 at least partially protrudes from a tool holder 26including, in part, an annular shoulder 28 and an annular spindle 30.Preferably, the shoulder 28 has a substantially cylindrical shape,although other suitable shapes may be used. Conventional shoulders 28,like conventional pin tools 16, are non-consumable, although aconsumable shoulder 28 may be used. The shoulder 28 may be made of amaterial that is similar to or dissimilar from those comprising theworkpiece 18, such as a refractory metal alloy (a molybdenum alloy, atungsten alloy, etc.) or the like. The shoulder 28 may be non-rotating,or may rotate in coordination with or independent of the pin tool 16.Like the pin tool 16, the shoulder 28 is typically rotated at a speed ofbetween about 100 rpm and about 1,500 rpm during friction stir welding,depending upon the materials 20,22 to be welded, via a drive mechanism(not shown). It should be noted that the rotational speed of theshoulder 28 is also dependent upon the thickness of the workpiece 18 tobe friction stir welded, with thinner sections requiring higherrotational speeds and thicker sections requiring lower rotationalspeeds. The shoulder 28 has an inside diameter that is slightly largerthan the diameter of the pin tool 16 in order to accommodate the pintool 16 without restriction and/or binding. The shoulder 28 has anoutside diameter that is about two to three times larger than thediameter of the pin tool 16, although any suitable dimensions may beused. The shoulder 28 protrudes from the tool holder 26 by about 0.5inches, although any suitable dimensions may be used. Both the shoulder28 and the pin tool 16 may be selectively and continuously extendablefrom/retractable into the tool holder 26, either in coordination with orindependent of one another. Accordingly, both the shoulder 28 and thepin tool 16 may incorporate and use axial load feedback control.

Preferably, the spindle 30 has a substantially cylindrical shape,although other suitable shapes may be used. The spindle 30 has an insidediameter that is slightly larger than the diameter of the pin tool 16and the drive mechanism (not shown) in order to prevent restrictionand/or binding. In the case of a consumable pin tool 16, the length ofthe spindle 30 is as short as possible in order to prevent spindlerun-out, which may affect the positional accuracy of the pin tool 16, aswell as weld quality/soundness. However, the length of the spindle 30 islong enough to allow a sufficient length of feedstock (i.e. pin tool 16)to be provided in order to produce a weld of useful continuous length.Preferably, the spindle 30 is made of tool steel or the like. The insidesurface of the spindle 30 defines one or more channels 32 through whicha cooling fluid flows. The one or more channels 32 may be partially orwholly aligned with the axis of the spindle 30. Alternatively, a singlechannel 32 may be substantially co-axial with the axis of the spindle30. The cooling fluid is operable for cooling the pin tool 16 and/or theshoulder 28 and consists of air, an inert gas, water, cooling oil,ethylene glycol, or any other suitable cooling fluid. Preferably, in thecase of a consumable pin tool 16, the temperature of the tip of the pintool 16 is maintained in a range in which the pin tool material issubstantially plastic. For example, the temperature of the tip of thepin tool 16 is maintained in a range of between about 1,650 degrees F.and about 1,990 degrees F. for titanium alloys and about 1,800 degreesF. and about 2,200 degrees F. for steel and nickel alloys. Likewise, ifa consumable shoulder 28 is used, the temperature of the shoulder 28 ismaintained in a range in which the shoulder material is substantiallyplastic. For example, the temperature of the shoulder 28 is maintainedin a range of between about 1,650 degrees F. and about 1,990 degrees F.for titanium alloys and about 1,800 degrees F. and about 2,200 degreesF. for steel and nickel alloys. In order to contain the cooling fluidwithin the one or more channels 32 in the presence of rotatingcomponents, one or more seals 34, such as o-ring seals or the like, areused. It should be noted that a cooling jacket (not shown) containingthe cooling fluid may also be disposed about the spindle 30 and used tocool the pin tool 16 and/or the shoulder 28. The cooling fluid flow rateto the one or more channels 32 and the cooling jacket (not shown) may bethe same or different, and may be controlled using one or moretemperature feedback loops or the like. Other suitable coolingmechanisms well known to those of ordinary skill in the art may also beused.

Although one preferred embodiment of the pin tool apparatus 12 has beenillustrated and described above, it should be noted that any suitablecomponents or apparatuses that provide a rotating or non-rotating,moveable or non-moveable, consumable or non-consumable pin tool 16 maybe used.

As described above, the pin tool 16 is plunged into the rigidly clampedworkpiece 18 and traversed along the joint 24 to be welded. The pin tool16 provides a combination of frictional heat and thermo-mechanicalworking to accomplish the weld. As the pin tool 16 is traversed alongthe joint 24 to be welded, the plasticized metal, metal alloy, or othermaterial is transferred from the leading edge of the pin tool 16 to thetrailing edge of the pin tool 16, forming a strong solid-state weldjoint 24 in the wake of the pin tool 16. In the case of a consumable pintool 16, the pin tool 16 is substantially continuously fed into thejoint 24 to be welded and is incorporated into the joint 24 as fillermaterial. Preferably, the pin tool 16 is fed into the joint 24 at a ratethat is sufficient to fill the joint preparation (e.g. square groove,v-groove, or j-groove) without underfill or substantial overfill.

The thermal management system 14 includes a heating member 36 disposeddirectly or indirectly adjacent to the joint 24 to be welded, oppositethe pin tool apparatus 12 relative to the workpiece 18. The heatingmember 36 consists of a ceramic strip heater (made of an alumina orsilica outer casing surrounding a heating element) or the like, capableof being heated to a temperature of between about 500 degrees F. andabout 2,500 degrees F., depending on the materials involved. Preferably,the heating member 36 has a width that is about equal to the width ofthe portion 38 of the workpiece 18 that is affected by the weldingprocess and a length that is about equal to the length of the joint 24to be welded. In general, thinner plates may be joined with heaterstrips that are relatively narrow, while thicker plates may be joinedwith heater strips that are relatively wide. The object is to heat thewidth at the root of the joint 24 to be welded that is stirred withoutexcessively heating the surrounding material and causing unnecessarythermal expansion and undesirable distortions. In an exemplaryembodiment of the present invention, the width of the heating member 36is between about 0.125 inches and about 1.5 inches, depending upon thebase material thickness, thermal conductivity, and high-temperaturestrength. Other suitable dimensions may be used. The heating member 36is disposed within a recess formed in a cooling member 40 and ispartially or wholly surrounded by a compliant insulation layer 42. Thecooling member 40 consists of a copper chill block or the like. In anexemplary embodiment of the present invention, the thickness of thecompliant insulation layer 42 is between about 0.02 inches and about0.125 inches, although other suitable dimensions may be used. Thecooling member 40 includes one or more cooling passages 44 through whicha cooling fluid flows. The cooling fluid is operable for controlling thetemperature of the heating member 36 and, in combination with thecompliant insulation layer 42, insulating the other components of thethermal management system 14 and the friction stir welding apparatus 10from the heat generated by the heating member 36. The cooling fluidconsists of air, an inert gas, water, cooling oil, ethylene glycol, orany other suitable cooling fluid. Preferably, the cooling member 40, thecompliant insulation layer 42, and the heating member 36 arecollectively disposed within a recess formed in a substantially rigidplate 46, such as a steel plate or the like, forming a welding table onwhich the workpiece 18 is disposed. Optionally, a hard metal backingsheet 48 is disposed between the surface of the substantially rigidplate 46 and the heating member 36 and the workpiece 18. Typically, thehard metal backing sheet 48 is made of a molybdenum alloy, a tungstenalloy, or the like, has a width of between about 0.125 inches and about1 inch, and has a thickness of between about 0.032 inches and about 0.05inches. Other suitable dimensions may be used. Preferably, the volume 50surrounding the joint 24 to be welded adjacent to the substantiallyrigid plate 46 and/or the hard metal backing sheet 48 is shielded fromthe surrounding atmosphere by a shielding mechanism 52, such as an inertgas shielding mechanism (FIG. 1) (using argon, helium, an argon/heliummixture, etc.), an inert powder shielding mechanism (FIG. 2) (using acomposition similar to the fluxes used for conventional submerged arcwelding, a custom composition engineered specifically for the basematerials to be joined, etc.), or the like. This shielding mechanism 52is required because, during the welding of certain materials, such astitanium alloys and the like, the materials may oxidize in the presenceof the surrounding atmosphere and the resulting oxides may becomeentrapped in the weld, compromising weld quality/soundness. It should benoted that any suitable shielding mechanisms 52 and/or atmosphericcontrols may be used.

As described above, the thermal management system 14 allows theworkpiece 18 to be controllably heated during friction stir welding,such that the temperatures in the workpiece 18 more closely match thetemperatures in the pin tool 16. In this manner, the cooling rate of theweld joint 24 may be controlled. This results in a weld joint 24 ofenhanced quality and mechanical integrity, free from defects andworkpiece distortions and demonstrating improved fracture toughness,impact strength, and fatigue properties. This also allows for enhancedpin tool temperature control in the event that a consumable pin tool 16is used and minimizes problems associated with pin tool debrisentrapment. Finally, pin tool wear is reduced and pin tool lifeincreased.

Referring to FIG. 3, in another embodiment of the present invention, thefriction stir welding apparatus 10 is as described above (FIGS. 1 and2), except that the thermal management system 14 includes a plurality ofheating members 36 disposed directly or indirectly adjacent to the joint24 to be welded, rather than the single heating member 36 disposeddirectly or indirectly adjacent to the joint 24 to be welded, oppositethe pin tool apparatus 12 relative to the workpiece 18. Each of theplurality of heating members 36 consists of a ceramic strip heater (madeof an alumina or silica outer casing surrounding a heating element) orthe like, capable of being heated to a temperature of between about 500degrees F. and about 2,500 degrees F., depending on the materialsinvolved. Preferably, each of the plurality of heating members 36 has awidth that is less than the width of the portion 38 of the workpiece 18that is affected by the welding process and a length that is about equalto the length of the joint 24 to be welded. In an exemplary embodimentof the present invention, the width of each of the plurality of heatingmembers 36 is between about 0.125 inches and about 0.75 inches,depending upon the base material thickness, thermal conductivity, andhigh-temperature strength. Other suitable dimensions may be used. Thethermal management system 14 also includes a hard metal backing strip 54disposed directly adjacent to the joint 24 to be welded, opposite thepin tool apparatus 12 relative to the workpiece 18. The hard metalbacking strip 54 is made of a substantially rigid material that iscapable of withstanding the relatively high temperatures generated bythe plurality of heating members 36, such as a molybdenum alloy, atungsten alloy, or the like. Preferably, the hard metal backing strip 54has a width that is less than the width of the portion 38 of theworkpiece 18 that is affected by the welding process and a length thatis about equal to the length of the joint 24 to be welded. In anexemplary embodiment of the present invention, the width of the hardmetal backing strip 54 is between about 0.125 inches and about 1 inch,and the thickness of the hard metal backing strip 54 is between about0.032 inches and about 0.25 inches. Other suitable dimensions may beused. The hard metal backing strip 54 serves a similar function to thehard metal backing sheet 48 (FIGS. 1 and 2) described above, supportingthe joint 24 to be welded.

Referring to FIG. 4, in a further embodiment of the present invention,the friction stir welding apparatus 10 is as described above (FIGS. 1and 2), except that the thermal management system 14 includes aresistance-heated hard metal backing strip 56 disposed directly adjacentto the joint 24 to be welded, rather than the single heating member 36disposed directly or indirectly adjacent to the joint 24 to be welded,opposite the pin tool apparatus 12 relative to the workpiece 18. Theresistance-heated hard metal backing strip 56 is made of a substantiallyrigid material, such as a molybdenum alloy, a tungsten alloy, or thelike, and is capable of being heated to a temperature of between about500 degrees F. and about 2,500 degrees F., depending on the materialsinvolved. Preferably, the resistance-heated hard metal backing strip 56has a width that is about equal to the width of the portion 38 of theworkpiece 18 that is affected by the welding process and a length thatis about equal to the length of the joint 24 to be welded. In anexemplary embodiment of the present invention, the width of theresistance-heated hard metal backing strip 56 is between about 0.25inches and about 3 inches, and the thickness of the resistance-heatedhard metal backing strip 56 is between about 0.032 inches and about 0.25inches. Other suitable dimensions may be used. The resistance-heatedhard metal backing strip 56 serves a similar function to the hard metalbacking sheet 48 (FIGS. 1 and 2) described above, supporting the joint24 to be welded.

Although the present invention has been illustrated and described withreference to preferred embodiments and examples thereof, it will bereadily apparent to those of ordinary skill in the art that otherembodiments and examples may perform similar functions and/or achievesimilar results. All such equivalent embodiments and examples are withinthe spirit and scope of the present invention and are intended to becovered by the following claims.

1. A friction stir welding apparatus operable for joining one or moresimilar or dissimilar materials forming a workpiece along a joint to bewelded, the friction stir welding apparatus comprising: a pin toolapparatus selectively disposed adjacent to and in direct contact with afirst surface of the workpiece along the joint to be welded; and aheating member disposed adjacent to a second surface of the workpiecealong the joint to be welded, the heating member operable forcontrollably heating at least a portion of the workpiece adjacent to thejoint to be welded.
 2. The friction stir welding apparatus of claim 1,wherein the heating member comprises a heating member selected from thegroup consisting of a ceramic strip heater, a plurality of ceramic stripheaters, and a resistance-heated hard metal backing strip.
 3. Thefriction stir welding apparatus of claim 1, wherein the heating memberis operable for generating a temperature of between about 500 degrees F.and about 2,500 degrees F.
 4. The friction stir welding apparatus ofclaim 1, wherein the heating member has a length that is about equal toa length of the joint to be welded.
 5. The friction stir weldingapparatus of claim 1, further comprising a cooling member disposed aboutat least a portion of the heating member, the cooling member operablefor controlling a temperature of the heating member.
 6. The frictionstir welding apparatus of claim 5, wherein an interior surface of thecooling member defines one or more cooling passages, the one or morecooling passages operable for containing a cooling fluid.
 7. Thefriction stir welding apparatus of claim 6, wherein the cooling fluidcomprises a cooling fluid selected from the group consisting of air, aninert gas, water, cooling oil, and ethylene glycol.
 8. The friction stirwelding apparatus of claim 5, further comprising a compliant insulationlayer disposed about at least a portion of the heating member, betweenat least a portion of the heating member and at least a portion of thecooling member, the compliant insulation member operable for insulatingthe heating member.
 9. The friction stir welding apparatus of claim 5,further comprising a substantially rigid plate disposed about at least aportion of the cooling member, the substantially rigid plate operablefor supporting at least a portion of the workpiece.
 10. The frictionstir welding apparatus of claim 1, further comprising a hard metalbacking strip disposed adjacent to the second surface of the workpiecealong the joint to be welded, the hard metal backing strip operable forsupporting at least a portion of the workpiece adjacent to the joint tobe welded.
 11. The friction stir welding apparatus of claim 1, furthercomprising a hard metal backing sheet disposed between the secondsurface of the workpiece and the heating member, the hard metal backingsheet operable for supporting at least a portion of the workpiece. 12.The friction stir welding apparatus of claim 1, further comprising ashielding mechanism disposed about the joint to be welded adjacent tothe first surface of the workpiece, the shielding mechanism operable forshielding the joint to be welded from a surrounding atmosphere.
 13. Thefriction stir welding apparatus of claim 12, wherein the shieldingmechanism comprises a shielding mechanism selected from the groupconsisting of an inert gas shielding mechanism and an inert powdershielding mechanism.
 14. The friction stir welding apparatus of claim 1,wherein the pin tool apparatus comprises a pin tool apparatus selectedfrom the group consisting of a non-consumable pin tool apparatus and aconsumable pin tool apparatus.
 15. The friction stir welding apparatusof claim 1, wherein the one or more similar or dissimilar materialscomprise one or more similar or dissimilar materials selected from thegroup consisting of one or more similar or dissimilar metals and one ormore similar or dissimilar metal alloys.
 16. A thermal management systemfor use with a friction stir welding apparatus operable for joining oneor more similar or dissimilar materials forming a workpiece along ajoint to be welded, the thermal management system comprising: a heatingmember disposed adjacent to a surface of the workpiece along the jointto be welded, the heating member operable for controllably heating atleast a portion of the workpiece adjacent to the joint to be welded. 17.The thermal management system of claim 16, wherein the heating membercomprises a heating member selected from the group consisting of aceramic strip heater, a plurality of ceramic strip heaters, and aresistance-heated hard metal backing strip.
 18. The thermal managementsystem of claim 16, wherein the heating member is operable forgenerating a temperature of between about 500 degrees F. and about 2,500degrees F.
 19. The thermal management system of claim 16, wherein theheating member has a length that is about equal to a length of the jointto be welded.
 20. The thermal management system of claim 16, furthercomprising a cooling member disposed about at least a portion of theheating member, the cooling member operable for controlling atemperature of the heating member.
 21. The thermal management system ofclaim 20, wherein an interior surface of the cooling member defines oneor more cooling passages, the one or more cooling passages operable forcontaining a cooling fluid.
 22. The thermal management system of claim21, wherein the cooling fluid comprises a cooling fluid selected fromthe group consisting of air, an inert gas, water, cooling oil, andethylene glycol.
 23. The thermal management system of claim 20, furthercomprising a compliant insulation layer disposed about at least aportion of the heating member, between at least a portion of the heatingmember and at least a portion of the cooling member, the compliantinsulation member operable for insulating the heating member.
 24. Thethermal management system of claim 20, further comprising asubstantially rigid plate disposed about at least a portion of thecooling member, the substantially rigid plate operable for supporting atleast a portion of the workpiece.
 25. The thermal management system ofclaim 16, further comprising a hard metal backing strip disposedadjacent to the surface of the workpiece along the joint to be welded,the hard metal backing strip operable for supporting at least a portionof the workpiece adjacent to the joint to be welded.
 26. The thermalmanagement system of claim 16, further comprising a hard metal backingsheet disposed between the surface of the workpiece and the heatingmember, the hard metal backing sheet operable for supporting at least aportion of the workpiece.
 27. The thermal management system of claim 16,further comprising a shielding mechanism disposed about the joint to bewelded adjacent to another surface of the workpiece, the shieldingmechanism operable for shielding the joint to be welded from asurrounding atmosphere.
 28. The thermal management system of claim 27,wherein the shielding mechanism comprises a shielding mechanism selectedfrom the group consisting of an inert gas shielding mechanism and aninert powder shielding mechanism.
 29. The thermal management system ofclaim 16, wherein the one or more similar or dissimilar materialscomprise one or more similar or dissimilar materials selected from thegroup consisting of one or more similar or dissimilar metals and one ormore similar or dissimilar metal alloys.
 30. A friction stir weldingmethod for joining one or more similar or dissimilar materials forming aworkpiece along a joint to be welded, the friction stir welding methodcomprising: selectively disposing a pin tool apparatus adjacent to andin direct contact with a first surface of the workpiece along the jointto be welded; disposing a heating member adjacent to a second surface ofthe workpiece along the joint to be welded; and controllably heating atleast a portion of the workpiece adjacent to the joint to be weldedusing the heating member.
 31. The friction stir welding method of claim30, wherein the heating member comprises a heating member selected fromthe group consisting of a ceramic strip heater, a plurality of ceramicstrip heaters, and a resistance-heated hard metal backing strip.
 32. Thefriction stir welding method of claim 30, wherein controllably heatingat least a portion of the workpiece adjacent to the joint to be weldedusing the heating member comprises controllably heating at least aportion of the workpiece adjacent to the joint to be welded to atemperature of between about 500 degrees F. and about 2,500 degrees F.33. The friction stir welding method of claim 30, wherein the heatingmember has a length that is about equal to a length of the joint to bewelded.
 34. The friction stir welding method of claim 30, furthercomprising disposing a cooling member about at least a portion of theheating member, the cooling member operable for controlling atemperature of the heating member.
 35. The friction stir welding methodof claim 34, wherein an interior surface of the cooling member definesone or more cooling passages, the one or more cooling passages operablefor containing a cooling fluid.
 36. The friction stir welding method ofclaim 35, wherein the cooling fluid comprises a cooling fluid selectedfrom the group consisting of air, an inert gas, water, cooling oil, andethylene glycol.
 37. The friction stir welding method of claim 34,further comprising disposing a compliant insulation layer about at leasta portion of the heating member, between at least a portion of theheating member and at least a portion of the cooling member, thecompliant insulation member operable for insulating the heating member.38. The friction stir welding method of claim 34, further comprisingdisposing a substantially rigid plate about at least a portion of thecooling member, the substantially rigid plate operable for supporting atleast a portion of the workpiece.
 39. The friction stir welding methodof claim 30, further comprising disposing a hard metal backing stripadjacent to the second surface of the workpiece along the joint to bewelded, the hard metal backing strip operable for supporting at least aportion of the workpiece adjacent to the joint to be welded.
 40. Thefriction stir welding method of claim 30, further comprising disposing ahard metal backing sheet between the second surface of the workpiece andthe heating member, the hard metal backing sheet operable for supportingat least a portion of the workpiece.
 41. The friction stir weldingmethod of claim 30, further comprising disposing a shielding mechanismabout the joint to be welded adjacent to the first surface of theworkpiece, the shielding mechanism operable for shielding the joint tobe welded from a surrounding atmosphere.
 42. The friction stir weldingmethod of claim 41, wherein the shielding mechanism comprises ashielding mechanism selected from the group consisting of an inert gasshielding mechanism and an inert powder shielding mechanism.
 43. Thefriction stir welding method of claim 30, wherein the pin tool apparatuscomprises a pin tool apparatus selected from the group consisting of anon-consumable pin tool apparatus and a consumable pin tool apparatus.44. The friction stir welding method of claim 30, wherein the one ormore similar or dissimilar materials comprise one or more similar ordissimilar materials selected from the group consisting of one or moresimilar or dissimilar metals and one or more similar or dissimilar metalalloys.
 45. A thermal management method for use with a friction stirwelding method for joining one or more similar or dissimilar materialsforming a workpiece along a joint to be welded, the thermal managementmethod comprising: disposing a heating member adjacent to a surface ofthe workpiece along the joint to be welded; and controllably heating atleast a portion of the workpiece adjacent to the joint to be weldedusing the heating member.
 46. The thermal management method of claim 45,wherein the heating member comprises a heating member selected from thegroup consisting of a ceramic strip heater, a plurality of ceramic stripheaters, and a resistance-heated hard metal backing strip.
 47. Thethermal management method of claim 45, wherein controllably heating atleast a portion of the workpiece adjacent to the joint to be weldedusing the heating member comprises controllably heating at least aportion of the workpiece adjacent to the joint to be welded to atemperature of between about 500 degrees F. and about 2,500 degrees F.48. The thermal management method of claim 45, wherein the heatingmember has a length that is about equal to a length of the joint to bewelded.
 49. The thermal management method of claim 45, furthercomprising disposing a cooling member about at least a portion of theheating member, the cooling member operable for controlling atemperature of the heating member.
 50. The thermal management method ofclaim 49, wherein an interior surface of the cooling member defines oneor more cooling passages, the one or more cooling passages operable forcontaining a cooling fluid.
 51. The thermal management method of claim50, wherein the cooling fluid comprises a cooling fluid selected fromthe group consisting of air, an inert gas, water, cooling oil, andethylene glycol.
 52. The thermal management method of claim 49, furthercomprising disposing a compliant insulation layer about at least aportion of the heating member, between at least a portion of the heatingmember and at least a portion of the cooling member, the compliantinsulation member operable for insulating the heating member.
 53. Thethermal management method of claim 49, further comprising disposing asubstantially rigid plate about at least a portion of the coolingmember, the substantially rigid plate operable for supporting at least aportion of the workpiece.
 54. The thermal management method of claim 45,further comprising disposing a hard metal backing strip adjacent to thesurface of the workpiece along the joint to be welded, the hard metalbacking strip operable for supporting at least a portion of theworkpiece adjacent to the joint to be welded.
 55. The thermal managementmethod of claim 45, further comprising disposing a hard metal backingsheet between the surface of the workpiece and the heating member, thehard metal backing sheet operable for supporting at least a portion ofthe workpiece.
 56. The thermal management method of claim 45, furthercomprising disposing a shielding mechanism about the joint to be weldedadjacent to another surface of the workpiece, the shielding mechanismoperable for shielding the joint to be welded from a surroundingatmosphere.
 57. The thermal management method of claim 56, wherein theshielding mechanism comprises a shielding mechanism selected from thegroup consisting of an inert gas shielding mechanism and an inert powdershielding mechanism.
 58. The thermal management method of claim 45,wherein the one or more similar or dissimilar materials comprise one ormore similar or dissimilar materials selected from the group consistingof one or more similar or dissimilar metals and one or more similar ordissimilar metal alloys.
 59. A friction stir welding apparatus operablefor joining one or more similar or dissimilar materials forming aworkpiece along a joint to be welded, the friction stir weldingapparatus comprising: an annular spindle having an interior portion andan axis, the interior portion of the annular spindle at least partiallydefining one or more cooling channels, the one or more cooling channelsoperable for containing a cooling fluid; a shoulder disposed adjacent tothe annular spindle and substantially aligned with the axis of theannular spindle; a pin tool disposed adjacent to the shoulder andsubstantially aligned with the axis of the annular spindle; and whereinthe cooling fluid is operable for cooling at least one of the shoulderand the pin tool.
 60. The friction stir welding apparatus of claim 59,wherein the shoulder is at least partially disposed within the annularspindle.
 61. The friction stir welding apparatus of claim 59, whereinthe shoulder comprises an annular shoulder.
 62. The friction stirwelding apparatus of claim 61, wherein the pin tool is at leastpartially disposed within the annular shoulder.
 63. The friction stirwelding apparatus of claim 59, wherein the shoulder and the pin tool areintegrally formed.
 64. The friction stir welding apparatus of claim 59,wherein the shoulder rotates at a predetermined rotational speed. 65.The friction stir welding apparatus of claim 59, wherein the pin toolrotates at a predetermined rotational speed.
 66. The friction stirwelding apparatus of claim 59, wherein the shoulder comprises aconsumable material.
 67. The friction stir welding apparatus of claim59, wherein the pin tool comprises a consumable material.
 68. Thefriction stir welding apparatus of claim 59, wherein the cooling fluidcomprises a cooling fluid selected from the group consisting of air, aninert gas, water, cooling oil, and ethylene glycol.
 69. The frictionstir welding apparatus of claim 59, further comprising one or moreannular seals disposed within the annular spindle, the one or moreannular seals operable for containing the cooling fluid.
 70. Thefriction stir welding apparatus of claim 59, further comprising acooling jacket disposed about the annular spindle, the cooling jacketoperable for containing an additional cooling fluid, wherein theadditional cooling fluid is operable for cooling at least one of theshoulder and the pin tool.
 71. The friction stir welding apparatus ofclaim 70, wherein the additional cooling fluid comprises a cooling fluidselected from the group consisting of air, an inert gas, water, coolingoil, and ethylene glycol.
 72. The friction stir welding apparatus ofclaim 59, wherein the one or more cooling channels are substantiallyaligned with the axis of the annular spindle.
 73. The friction stirwelding apparatus of claim 59, wherein the one or more cooling channelscomprise a single cooling channel that is substantially co-axial withthe axis of the annular spindle.